Starting aids for discharge lamps can be characterized by two generic classes, viz: active devices such as pulse generators of one form or another; and passive techniques such as ground planes or probes.
Active devices have the disadvantage of being costly; further, they contribute to the size and weight of the ballast package. The active devices also tend to be complex with this complexity adding a negating factor since the reliability is adversely affected.
Passive starting aids also can be broken down into two distinct classes. First, there is the external type which comprised ground planes adjacent to or in contact with the exterior bulb wall. Examples of this type of starting aid include external conductive bulb wall coatings or stripes and grounded fixtures. The second class of passive starting aids includes internal conductive stripes or coatings and starting probes.
The relative merits of a particular type of passive starting aid depends on the lamp type and the intended market application. For example, the standard F40WT12 lamp relies generally on a grounded fixture to provide the necessary starting function. Energy saving, krypton-filled, F34WT12 lamps rely on an internal conductive film applied between the glass and the phosphor. External stripes and coatings have found favor in Europe.
However, while the use of starting aids has been recognized as a desirable feature, it has not been heretofore possible to provide non-linear, "formed lamps," i.e., circular, with an effective and economical internal starting aid.